This invention rlates to the field of metallurgy, and particularly to the field of processing aluminum alloys which have precipitating and dispersoid forming constituents.
Fine grain aluminum alloys have been produced by a three step, thermo-mechanical process (overaging, deformation, and recrystallization) such as described in U.S. Pat. No. 4,092,181. This prior art process and later modifications such as described in U.S. Pat. Nos. 4,222,797; 4,295,901; 4,358,324; 4,490,188; 4,486,242; and 4,486,244 have produced grains as small as 8 .mu.m in thin sheet material. The fine grain material has good ductility and is capable of being superplastically formed. Although the prior art process has proven very useful for fabricating fine grain sheet, the large amount of deformation required has presented a problem in obtaining fine grain in heavy sections such as heavy plate, bar, and forging stock. Additionally, prior attempts to provide ultrafine grain size (about 2 .mu.m) have not been successful.